The present invention relates to a webbing tension sensor and more particularly to a webbing tension sensor that detects changes in the tension within a webbing, for example, a seat belt webbing, to enable operation of safety and other devices.
Most vehicles today are equipped with safety devices. One of the earliest and arguably most effective of these devices is the seat belt. Historically, as automobiles became increasingly pervasive, it soon became apparent that people riding in vehicles had a much better chance of surviving a crash if they remained with the vehicle. Early race car drivers pioneered the use of safety restraints, and eventually this important safety feature made its way into the consumer market as the seat belt. Seat belt use is mandatory in many states in the United States.
Now many other safety devices such as air bags and crash warning systems are becoming more commonplace. One of the difficulties associated with the operation of these devices is determining when they need to activate. Air bags have been particularly troublesome due to the explosive reaction necessary to deploy them in an effective time period. Children and smaller adults have been injured and even killed by a deploying air bag. It is essential for all these safety devices to operate reliably and at the proper time. Many methods have been employed in the past to meet these requirements and because seat belt use is becoming pervasive, it is natural for manufacturers of vehicles and safety devices to exploit seat belt tension as a way to determine the need for further action.
Seat belt tension is affected by accelerating forces, many of which are generated in an emergency situation. Designing a simple, low cost device that reliably measures seat belt tension has proven difficult. Past devices generally include many moving parts with sensitive components which are difficult to calibrate. The same is true of other devices which utilize an internal mass to detect accelerating forces. Additionally, special mounting brackets must be used to equip the vehicle with the prior art devices.
There is a need for a simple, yet reliable device that is compact, easy to calibrate and does not require specialized mounting anchors, to monitor seat belt tension in order to trigger safety and other devices in response to changes in seat belt tension.
It is an object of the present invention to provide a reliable seat belt tension sensing unit that has relatively few moving parts. It is another object of the present invention to provide a seat belt tension sensing unit that is inexpensive to manufacture.
It is yet another object of the present invention to provide a seat belt tension sensing unit that can be used without modifying the webbing anchors currently used by a seat belt.
It is a further object of the present invention to provide a seat belt tension sensing unit that uses a small number of springs to detect the tension in a seat belt.
It is yet a further object of the present invention to provide a seat belt tension sensing unit that uses a hall effect sensor that is easily calibrated in order to decrease the manufacturing tolerances required for reliable use thereby decreasing the cost to produce the unit.
It has been found that the objects of the present invention can be met by a seat belt tension sensing unit that includes a hinge arm pivotally connected to a base. The hinge arm is elastically biased against a segment of seat belt webbing that passes through an opening in a cover which encloses the unit. As the tension changes in the webbing, a hall sensor detects the movement of a magnet attached to the hinge arm. Signals generated by the hall sensor are used for analysis as part of a system to determine if the air bag should be deployed in an emergency.
It has been further found that the objects of the present invention can also be met by a seat belt tension sensing unit that includes a fixed anchor portion and a movable anchor portion and at least one elastic element such as a spring. The elastic element is moveably mounted between the fixed and movable anchor portions. Seat belt webbing is connected to the movable anchor portion and a sensor detects the movement of a magnet that moves with the movable anchor portion as a function of the tension in the webbing. Signals generated by the sensor are used for analysis as part of a system to determine if the air bag should be deployed in an emergency.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.